Figure 105: Synchronization Lock Robustness Measurement - Analog Devices ADV7850 Hardware Manual

The measurements are performed on a line-by-line basis on all video lines but not during the VBI. For video lines during the VBI, the
result of the last active video line is kept.
The isd[8:0] value changes dynamically on a line by line basis; the ifsd[8:0] is an averaged version of the isd[8:0]. The averaging length can
be set to 128 or 256 lines of video.
isd_thr[7:0], Addr 44 (CP), Address 0x83[7:0]
This control is used to set the threshold used for the ISD measurement. Isd_thr[7:0] stores a 12-bit unsigned value.
Function
isd_thr[7:0]
0x00 
>0x01
ifsd_avg, Addr 44 (CP), Address 0x84[0]
This control is used to set the averaging mode used to compute ifsd[8:0].
Function
ifsd_avg
0 
1
isd[8:0], Addr 44 (CP), Address 0xE3[0]; Address 0xE4[7:0] (Read Only)
This readback represents the area of the HSync that falls below the slicing threshold set by isd_thr[7:0]. A high value indicates robust
locking.
Function
isd[8:0]
xxxxxxxxx
ifsd[8:0], Addr 44 (CP), Address 0xE3[1]; Address 0xE5[7:0] (Read Only)
This readback displays the average value of the ISD measurement over 128 or 256 lines. The number of lines used to compute ifsd[8:0]
is set in ifsd_avg.
Function
ifsd[8:0]
xxxxxxxxx
Rev. A May 2012
video signal
ISD[8:0] value represents
area value

Figure 105: Synchronization Lock Robustness Measurement

Description
Calculate threshold automatically and set to (level of HSync tip) + 0.5 * (HSync depth)
Set threshold to (isd_thr[7:0] * 8)
Description
isd[8:0] averaged over 128 lines of video to generate ifsd[8:0]
isd[8:0] averaged over 256 lines of video to generate ifsd[8:0]
Description
Readback value
Description
Readback value
HS detection threshold
as per ISD_THR[7:0]
297
ADV7850